Here is an interesting "Free Spotting" device that another lifter sent me information on. He has it at his gym and uses it.
It remind me of the ProSpot that I once sold at a fitness store that I worked at. http://youtube.com/watch?v=OvloqsfOtTQ
The ProSpot has a sensor in the handles that is run by electricity. When contact is make with the sensor on the bar, it allows the bar to move up and down, back and forth.
When you take you hand off the sensor, the cables lock and the bar stays where every you released you hands.
Another piece of equipment that is similar is the Hoist PTS 1000 Smith Machine. It moves vertically and horizonally.
Here is the Hoist.
http://www.hoistfitness.com/products/co ... 90&pid=317